Is it obligatory to remove the usurious increment from inherited money that was deposited in a usurious bank and spent on marriage, given the ignorance of the Sharia ruling at that time?

If the government deposits the father's pension in a usurious bank, and interest accrues from it, then this interest is unlawful for the heirs. It must be spent on general Muslim welfare or given to the poor and needy. They are not permitted to spend it on themselves unless they are poor and in need, in which case they may take from it according to their necessity.

If the heirs spent this interest while unaware of its unlawfulness, then ignorance absolves them of sin. However, it does not absolve them of the obligation to ensure these interests reach their rightful recipients. If they spent it while they were poor, there is nothing due from them. But if they spent it while they were wealthy, then they must disburse it for charitable purposes.